Dear all:

I would like to understand more about iqdmrg. I hope you can help me. Thanks in advance. The questions are listed as below.

Is it correct that iqdmrg is a U(1) symmetric dmrg program?

Take heisenberg chain as an example, the quantum number of the tensor index in the center of the chain is truncated. I would like to know how you do this. For example, one tensor at site 49 shown below. I suppose that for this tensor there also quantum numbers like QN(49), QN(48),... but here they are definitely truncated.

/--------------IQTensor--------------

r=3 div=QN(0) log(scale)=0

IQIndex(d,8,Link,7) < Out >

(d1,1,Link,822) QN(3)

(d2,3,Link,201) QN(1)

(d3,3,Link,631) QN(-1)

(d4,1,Link,125) QN(-3)

IQIndex(S=1/2 49,2,Site,338) < Out >

(Up 49,1,Site,810) QN(1)

(Dn 49,1,Site,550) QN(-1)

IQIndex(d,8,Link,551) < In >

(d0,1,Link,410) QN(4)

(d1,3,Link,691) QN(2)

(d2,3,Link,705) QN(0)

(d3,1,Link,921) QN(-2)

\ ------------------------------------

- I also tested with pure external magnetic form
`H= \sum h*S^z`

. The ground state shows that the total quantum number of the wave function is QN(0), which concerned me a lot since I expect the quantum number of the chain should be QN(N). Is that correct?

Sorry for the massive contents, and probably trivial questions listed above. But I do want to know more on this. Any comments are welcomed. Thanks very much.

Best Regards

Wangwei Lan

Thanks very much for the detailed explanation. These are very helpful to me. I think now all these things are clear to me.